In vehicle headlights of more recent design, a plurality of stepper motors are used in order to move desired headlight parts to desired positions.
It is known, for example, to use a stepper motor to regulate the headlight range of the headlight.
It is furthermore already known to move a trim using a solenoid in order to switch between low beam and high beam.
Furthermore, headlights with a bending light function are already known. Here, a drive is used to rotate the entire optical construction of the headlight. The rotary movement is limited in both directions by end stops.
It is also known to perform driving of a trim of the headlight using a stepper motor. In this case, the trim is moved to the right or left and/or up or down.
It is also already known to insert a rotatable prism horizontally into the beam path of the headlight. Such a prism is driven using a stepper motor. By rotating the prism, a more or less continuously variable transition between low beam and high beam can be realized. Such a headlight has a Hall sensor, the output signals of which are used to position the rotatable prism. In case of a defect of the Hall sensor, the rotatable prism has a stop element, using which the prism can be positioned by way of rotation at a stop counter element. The rotatability of the prism is limited by the cooperation of stop element and stop counter element. Full rotation of the prism is not possible.
One example of such a rotatable prism is illustrated in FIG. 1. It has various rotary positions. A first rotary position D1 is associated with a symmetrical light distribution, a second rotary position D2 with the low beam, a third rotary position D3 with the motorway light and a fourth rotary position D4 with the high beam of the respective vehicle headlight. Located at a fifth rotary position, provided between the rotary position D4 that is associated with the high beam and the rotary position D1 that is associated with the symmetrical light distribution, is the aforementioned stop element AE1. Switch edges SF derived from the output signal of the Hall sensor occur between the first and the second rotary position and between the third and the fourth rotary position. The aforementioned stop element AE1 furthermore ensures during operation of the headlight that a transition from symmetrical light distribution to high beam and vice versa cannot occur.
The prism PR shown is a constituent component of a vehicle headlight which additionally has a reflector R, a light source Q arranged inside the reflector, and a lens L.
It is furthermore already known to capture the oncoming traffic using a camera and to maintain a switched-on high beam, but to dim that region in which oncoming vehicles are situated so as not to blind the oncoming traffic. To realize such a partial high beam, the function partial high beam is associated with a further rotary position of the rotatable prism. The exact position of the screened portion is determined by the bending light function. However, in this case the stop element AE1 shown in FIG. 1 must be removed since not only must it be possible to change from the partial high beam to the high beam, but it must also be possible to change from the partial high beam to the low beam, where the latter change must not proceed via the high beam. One example of such a rotatable prism is illustrated in FIG. 2.
The prism PR shown by way of example in FIG. 2 is likewise a constituent component of a vehicle headlight which additionally has a reflector R, a light source Q arranged inside the reflector, and a lens L. It, too, is rotatable into different rotary positions. A first rotary position D1 is associated with a symmetrical light distribution, a second rotary position D2 with the low beam, a third rotary position D3 with the motorway light, a fourth rotary position D4 with the high beam, and a fifth rotary position D5 with the partial high beam. The stop element AE1, shown in FIG. 1, is not provided in the prism shown in FIG. 2. Switch edges SF derived from the output signal of the Hall sensor occur between the first and the second rotary position and between the third and the fourth rotary position. The absence of the stop element shown in FIG. 1 allows—as has already been discussed—a transition between low beam and partial high beam.
The prism shown in FIG. 2 operates without problems as long as the Hall sensor operates correctly and provides output signals, on the basis of which the rotary position of the prism can be ascertained. If the Hall sensor fails, however, the rotary position of the prism can no longer be ascertained. Owing to the construction of the vehicle headlight, it is also not possible in that case to set a rotary position of the prism that reliably does not blind the oncoming traffic. Although the rotary position of the prism should not change by itself owing to the detent torque of the drive of the prism, it cannot be ruled out that information relating to the instantaneous rotary position of the prism is lost on account of mechanical stress, of vibration, electrical faults, a power loss during the movement, manual interference or a cable break of a stepper motor coil.